Unpacking extension (Re: A small inconsistency in syntax?)

[Bernhard Herzog]

me at mikerobin.com (Michael Robin) writes:

> I'd think there's no reason to disallow it. 
> Although in Python the comma operator creates tuples 
> rather than the parens, for many it looks as if
>    a,b = seq 
> is just shorthand for 
>    (a,b) = seq

This version would not be removed. You need some kind of grouping to
support nested unpackings.

> and if it unpacks lists too (which it does)
> you may as well have the option of being
> explicit in your LHS pattern.

Why, if it doesn't make a difference at all?

a, b = t
(a, b) = t
[a, b] = t

are completely equivalent. They all generate the same bytecode and work
for all kinds of sequences with length 2.

> Also, given that lists are mutable and tuples are
> not, the list notation makes some kind of sense,
> even though you're rebinding the names in the LHS
> rather than creating a list, per se.

In my eyes the mutability of the RHS doesn't enter into it. All that
matters is that it's a sequence of the right length.

   Bernhard

-- 
Intevation GmbH                                 http://intevation.de/
Sketch                                 http://sketch.sourceforge.net/
MapIt!                                               http://mapit.de/